The current methods for producing potassium sulfate start with sulfuric acid and use either a high temperature reaction of potassium chloride with concentrated sulfuric acid, or use solvent extraction techniques to remove hydrochloric acid from the solution in methods in which potassium chloride and aqueous sulfuric acid are reacted.
U.S. Pat. Nos. 3,998,935 and 4,045,543 disclose the reaction of potassium chloride, directly or indirectly, with sulfuric acid in suitable solutions to produce potassium sulfate. In the first U.S. Pat. No., 3,998,935, the potassium chloride is reacted with a hot solution of potassium bisulfate to produce potassium sulfate which is recovered by cooling the solution. The hydrogen chloride produced remains in the mother liquor which is recycled to a potassium bisulfate production unit. The production of potassium bisulfate must be about 30 to 50% greater than the required sulfate output and an alternative use must be found for the excess bisulfate.
The second U.S. Pat. No., 4,045,543, describes a method whereby potassium sulfate is produced from sulfuric acid and potassium chloride added to a dilute solution containing H.sup.+, K.sup.+, Cl.sup.- and SO.sub.4.sup.-- ions. To remove the hydrogen chloride produced by the reaction, it must be distilled from the solution. Because of the manner in which the process is operated, a very large amount of water must be removed to remove the hydrogen chloride producing a distillate containing only about 5% HCl. Water must be removed from the distillate to concentrate the hydrogen chloride solution sufficiently for subsequent sale or use. A further major quantity of water equal to that removed by distillation is needed to wash the product, said to be potassium sulfate, produced upon cooling the reaction mixture. All in all, about 10 tons of water must be evaporated for each ton of potassium sulfate produced.